The teenager, from Eastern European, worked as a prostitute, seeing 65 to 70 customers a day.

The report comes as the police carried out raids access the capital, where more than 100 cases of trafficking are dealt with per year.

According to the Inter-Departmental Ministerial Group on human trafficking organised criminal gangs within countries including China, Nigeria, Vietnam, Slovakia and Romania now pose the greatest threat to the UK, where they exploit their victims for sex, labour and domestic slavery.

Barnardo’s chief executive Anne Marie Carrie said: “Policing of child trafficking is improving but it is still very patchy.

"We work with children who have been trafficked into the country and around the country for sex.

"Right now candidates are canvassing for election to be Police and Crime Commissioners and Barnardo’s is calling on them to put child sexual exploitation at the top of their agenda with our Cut them free campaign.

“Urgent action is needed to protect the hundreds of young girls and boys who are being trafficked, abused, raped and exploited for sex.

“We can all do more to protect the children and young people in our lives and in our communities from this increasingly organised and vile abuse.”

The Met police's Detective Insp Kevin Hyland has said the "vast majority" of victims think they're coming to a better life in the UK.

In response to the warnings, immigration minister said Mark Harper told BBC's 5 Live the report would "increase the awareness of what's going on."

"We're doing a better job of cracking down people involved in the vile trade, which is effectively modern-day slavery," he said.